1. Field of the Invention
The present invention relates to a physical quantity computation program and a storage medium for storing the physical quantity computation.
2. Description of the Related Art
According to Large Eddy Simulation (LES) that is one of highly accurate numerical analysis methods of a turbulent flow (“Study of enhancing the accuracy of a gradient diffusion type thermal flux model on the basis of LES data”, Transactions of the Japan Society of Mechanical Engineers, Vol. 64, No. 623, B(1998), page 2208-2215), by subjecting a dominating equation to a grid filter, turbulent components (GS components) larger in scale than a grid filter size are directly computed and turbulent components smaller in scale than the grid filter size are modeled and solved by a sub-grid scale (SGS) model. Hence, the computation accuracy of the LES heavily depends on the accuracy of the used SGS model. Most of the typical SGS models are based on eddy viscosity approximation and are modeled by giving turbulent viscosity. At this time, it is said that the turbulent viscosity needs to be multiplied by a wall-damping function to consider the wall effect near the surface of the wall. That is, when the whole fluid including fluid near the surface of the wall is analyzed by a turbulent model that assumes a sufficiently turbulent flow field away from the surface of the wall, a turbulent viscosity becomes too large in the fluid near the surface of the wall. Hence, to express a damping effect near the surface of the wall, a wall-damping function is used. Therefore, it is well known that the way this wall-damping function is given has a significant effect on the accuracy of computation.
By the way, in addition to the LES, a method of using a k-ε model is well known as a method of analyzing a turbulent flow. Even the k-ε model needs the above-described wall-damping function. It is reported that as for a wall-damping function of the K-ε model, when a Kolmogorov's velocity scale is used as a parameter, an appropriate wall-damping function can be constructed.
In this regard, turbulent variation has the property of being dissipated at a certain wave number by the molecular viscosity of fluid and the Kolmogorov's velocity scale is a velocity scale closely related to this wave number and is expressed by the use of the dissipation rate ε of turbulent energy.
Here, it is also thought that the above-described wall-damping function using the Kolmogorov's velocity scale is used not in the K-ε model but in the LES.
However, in the LES, as described above, only the turbulent components smaller in scale than the grid filter size are modeled and solved and the dissipation rate ε of turbulent energy is not solved, so that the above-described wall-damping function using the Kolmogorov's velocity scale can not be used as it is.
Hence, in the LES, in the case of using the above-described wall-damping function using the Kolmogorov's velocity scale, it is proposed that in place of the dissipation rate ε of the whole turbulent energy, the dissipation rate of SGS turbulent energy for the components of wave numbers smaller in scale than the grid filter size is used.
However, the dissipation rate of SGS turbulent energy for the components of wave numbers smaller in scale than the grid filter size is smaller in scale than the dissipation rate ε for the components of all wave numbers of the turbulent energy and depends on the grid size. Hence, when the above-described wall-damping function is specified by the use of the dissipation rate of SGS turbulent energy for the components of wave numbers smaller in scale than the grid filter size, an appropriate damping effect can not be produced and the wall-damping function becomes one heavily depending on the grid size used for computation, which results in reducing the accuracy of computation.